Look I though about this for some time. Now what i understood is you are struggling indeed to input a F-smash and u use tilt-button and if u had an option to use both smash button and tilt button at the same time that'll help am i right?
But that's impossible due to the game's limited controls option so I'll help u in a way that keep the smash button but instead of a full tilt button u can have an U-tilt and a D-tilt button (idk if u r comfortable with the normal side tilt with the A button) by adjusting the A second button and Up second button as the same input (that worked for my friend who's struggling when inputing the U-tilt)
I think that's all (i hope it's not too long for u to read💀🙏)